1. Field of the Invention
The present invention relates to a thin-film magnetic head and a method of manufacturing the same, and to a head assembly and a magnetic disk drive each of which includes the thin-film magnetic head.
2. Description of the Related Art
For magnetic read/write devices such as magnetic disk drives, higher recording density has been constantly required to achieve a higher storage capacity and smaller dimensions. Typically, thin-film magnetic heads used in magnetic read/write devices are those having a structure in which a reproducing (read) head having a magnetoresistive element (that may be hereinafter referred to as an MR element) for reading and a recording (write) head having an induction-type electromagnetic transducer for writing are stacked on a substrate.
Write heads include those of a longitudinal magnetic recording system wherein signals are magnetized in the direction along the surface of the recording medium (the longitudinal direction) and those of a perpendicular magnetic recording system wherein signals are magnetized in the direction perpendicular to the surface of the recording medium. Recently, the shift from the longitudinal magnetic recording system to the perpendicular magnetic recording system has been promoted in order to achieve higher recording density of magnetic read/write devices.
One of known magnetic heads for the longitudinal magnetic recording system has a configuration in which there are provided a bottom pole layer, a top pole layer, and a flat, spiral-shaped coil having a portion disposed between the bottom pole layer and the top pole layer, as disclosed in JP 2000-155913A, for example. In this magnetic head, the bottom pole layer and the top pole layer have their respective end faces located in a medium facing surface, with a predetermined distance provided between these end faces. Furthermore, the bottom pole layer and the top pole layer are joined to each other at a position away from the medium facing surface. The joint between the bottom pole layer and the top pole layer is located in a region inside the coil.
A magnetic head for the perpendicular magnetic recording system incorporates, for example, a flat, spiral-shaped coil and a pole layer, the pole layer allowing a magnetic flux corresponding to a magnetic field generated by the coil to pass therethrough and generating a write magnetic field for writing data on a recording medium. Another known magnetic head for the perpendicular magnetic recording system further incorporates an upper magnetic layer having a shield function, as disclosed in U.S. Pat. No. 7,126,788 B1, for example. In this magnetic head, the pole layer and the upper magnetic layer have their respective end faces located in the medium facing surface, wherein the end face of the upper magnetic layer is located forward of the end face of the pole layer with a predetermined distance provided therebetween. Furthermore, the pole layer and the upper magnetic layer are joined to each other at a position away from the medium facing surface. The joint between the pole layer and the upper magnetic layer is located in a region inside the coil.
As described above, for each of the longitudinal magnetic recording system and the perpendicular magnetic recording system, examples of magnetic heads include one that incorporates two magnetic layers and a flat, spiral-shaped coil. Here, in such a magnetic head, one of the two magnetic layers that is closer to the substrate is referred to as a lower magnetic layer while the other one of the magnetic layers is referred to as an upper magnetic layer. An example of a specific configuration of such a magnetic head will now be described. In this example, the magnetic head incorporates a lower magnetic layer, a flat, spiral-shaped coil insulated from the lower magnetic layer, an insulating layer covering this coil, and an upper magnetic layer that touches the insulating layer and is disposed such that part of the coil is sandwiched between the upper and lower magnetic layers. The insulating layer is toroidal in shape. The upper magnetic layer has a recessed portion that enters the space inside the toroidal insulating layer and that is joined to the lower magnetic layer.
It is known that magnetic heads may suffer such a phenomenon that heat generated by a coil causes a magnetic layer to expand and the end face of the magnetic layer located in the medium facing surface thereby protrudes toward the recording medium. To suppress the amount of protrusion of the end face of the magnetic layer, it is effective to reduce the resistance of the coil. To achieve this, it is effective to minimize the region inside the flat, spiral-shaped coil. A reduction in dimensions of the region inside the coil leads to a reduction in volume of the space inside the toroidal insulating layer mentioned above.
Consideration will now be given to the volume of the space inside the toroidal insulating layer mentioned above. As previously mentioned, the upper magnetic layer has the recessed portion that enters the space inside the toroidal insulating layer and that is thereby joined to the lower magnetic layer. As a result, if the above-mentioned space is too small, the joint between the upper and lower magnetic layers is reduced in area, and this causes a problem that the flow of a magnetic flux passing through the upper and lower magnetic layers is hindered. Furthermore, if the space is too small, it is difficult to form without defects the recessed portion of the upper magnetic layer to be disposed in the space and a portion of another layer to be disposed on the recessed portion. This can result in a reduction in reliability of the magnetic head.
On the other hand, if the above-mentioned space is too large, the coil increases in length and thus the resistance of the coil increases, which causes the previously-mentioned phenomenon that the end face of the magnetic layer protrudes toward the recording medium to occur noticeably.
Furthermore, it is assumed that the shapes of portions of the upper and lower magnetic layers around the joint between the upper and lower magnetic layers have an influence on the flow of a magnetic flux passing through the joint between the upper and lower magnetic layers, and thereby exert an influence on the write characteristics of the magnetic head.
As described above, it is assumed that the volume of the space inside the toroidal insulating layer and the shapes of the portions of the upper and lower magnetic layers around the joint between the upper and lower magnetic layers have an influence on the characteristics and reliability of the magnetic head. Conventionally, however, no detailed consideration has been given to these factors.